Cutting insert with grouped chip-forming ribs arranged symmetrically and having tapering cross sections

ABSTRACT

Cutting inserts are provided at their rake faces with a plurality of raised chip-forming elements in the form of longitudinal ribs which can be notched to have longitudinally-separated segments and at least some of which are parallel to one another.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/DE 92/00410 filed 14 May1992 and based in turn, upon German national application P 41 18 068.8filed 1 Jun. 1991 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a polygonal or circular cutting insert forchip-forming machining, which is provided at its rake faces with aplurality of raised chip-forming elements with upwardly decreasing crosssections and which are arranged in rows at a distance from the cuttingedges.

BACKGROUND OF THE INVENTION

Such cutting inserts are known for instance from DE-A 22 31 631, DE-B 2309 443 and the DE 31 48 535 C2.

DE-A 22 31 631 describes a cutting tool with chip breaker, with acutting blade attached to the basic chip-breaker body and with a grooverunning parallel and next to the cutting blade, wherein at least oneprojection shaped like a truncated cone is provided at a point locatedclose to the nose-like part of the basic chip-breaker body.

According to DE-B 23 09 443, in the chip-breaker groove a plurality ofchip-breaking projections is provided, consisting of sphere segmentsarranged at intervals.

However, due to the arrangement of the chip-forming elements and thegeometry of the chip-breaking groove, the mentioned cutting insert canbe used only within a limited range of different cutting conditions,such as different cutting depths, advance speeds, and materials. Inorder to increase the range of use of the cutting insert and to improvethe formation and removal of the chips, DE 31 48 535 C2 has proposed togive the chip-forming elements the basic shape of a truncated pyramid,with an essentially triangular base surface, whereby at any time one ofthe lines defining the base surface is oriented in the direction of theneighboring cutting edge, either parallel thereto or in a curved line.

OBJECTS OF THE INVENTION

It is an object of the present invention to further improve a cuttinginsert, so that the chip control in the area of the cutting edge isenhanced.

Another object is to provide a new geometry of the chip-forming elementsso that the friction between the removed chip and the rake face isreduced as much as possible, in order to avoid undesirable heating ofthe cutting insert while in use.

SUMMARY OF THE INVENTION

These objects are attained in a polygonal cutting insert whose raisedchip-forming elements are designed as longitudinal ribs, withlongitudinal axes are substantially perpendicular to the cutting edge orat an acute angle to a plane normal to the cutting edge, and of which atleast one of the groups of longitudinal ribs consisting of every otherlongitudinal rib are mutually parallel.

From U.S. Pat. No. 4,710,069 a cutting element is known with a clearanceface, as well as a rake face with a chamfer and a thereto subsequentcurved chip-forming surface, wherein a number of depressions arrangedalong each other and separated within the cutting edge are provided, inorder to bridge the borderline between the chamfer and the subsequentcurved rake face, whereby segments of the rake face are formed betweenthe depressions at the height of the cutting edge, but in the depressionareas deposits of chipped away material can form, which would finallylead to a metallic friction with the chip. This in turn increases theheating of the cutting insert, leading to increased wear.

While according to U.S. Pat. No. 4,710,069 the depressions extendlongitudinally in a perpendicular direction-with respect to the cuttingedge, EP 0 404 744 A2 proposes to arrange the depressions so that theyextend longitudinally in a direction set at an angle between 5° and 45°with respect to a line perpendicular to the cutting edge. Usually thechip flow angle has a value between 5° to 125°. But even this measurecan not prevent the gradual clogging of the depressions during themachining process, so that the respective rake face is "flattened" withincreased use.

The present invention completely turns away from the principle ofdepression formation, and replaces the depressions with raisedchip-forming elements designed as longitudinal ribs. Due to the factthat they extend further towards the middle of the cutting plate, theselongitudinal ribs have the advantage that even for various cuttingconditions with different cutting depths, even at a greater distancefrom the cutting edge the chip is still controlled and guided withlittle friction by the longitudinal ribs. In particular, thelongitudinal ribs have the advantage of very good heat dissipation, sothat a heating of the cutting insert in the cutting edge area issubstantially reduced.

So for instance it has proven advantageous to impart to the longitudinalribs a shape with an edge-free, convex cross section perpendicularly tothe longitudinal axis of rib in an area located above the rake faceplane. Preferably the convex shape should have a radius of 0.1 to 2 mmin the upper area, and even more preferably of 0.1 to 1.0 mm. Inrelation to a line perpendicular to the rake face, the longitudinal ribsrun perpendicularly with respect to their longitudinal axis in the areaof the rake face plane at an angle of at least 45°.

This can be achieved by providing a larger radius in the respective facearea than in the upper area or by imparting a flat shape to therespective rib surface piece, which means that in cross section the ribsurfaces run in a straight line to the rake face. Preferably in the areaof the rake face, the lateral surfaces of the longitudinal ribs form anangle of 90° to 130°, seen in cross section parallel to the cuttingedge. All the above-mentioned measures, considered individually orcombined, serve for creating the smallest possible, but edgeless,contact surface between the longitudinal ribs as chip-forming elementsand the removed chip, and on the other hand to increase the rib area somuch that the friction heat generated during chip-removal can be largelydissipated over this area. This purpose is also served by the measure ofselecting a corresponding base width of the longitudinal ribs in thearea of the rake face. For milling tools the preferred base width is 0.2to 0.5 mm, and for turning or drilling tools it is 0.5 to 1.5 mm.

Optimally with respect to the geometry of the chip-forming elements, theheight of the longitudinal ribs in cutting insert for milling tools is0.02 to 0.07 mm, and for turning or drilling tools it is 0.1 to 0.6 mm.

As has already been mentioned before, longitudinal ribs have theadvantage that even in areas remote from the cutting edge the chip canbe formed and controlled by the chip-forming elements. A preferredlength for the longitudinal ribs has proven to be a value wherein therespective length is 5 times to 20 times greater than the base width ofthe longitudinal ribs.

The different fields of use of the cutting insert determine also thedistance between two neighboring longitudinal ribs, which preferably is0.5 to 1.5 mm for milling tools and 1.5 to 4 mm for turning or drillingtools. However these dimensions are also to be considered each time inrelation to the aforementioned longitudinal rib height and depend on thefield of use of the cutting insert.

A particularly suitable shape for a longitudinal rib has proven to bethe configuration derived from an ellipsoid of revolution. Thereby thelongitudinal ribs represent substantially the cap of an ellipsoid ofrevolution cut off along a plane parallel with the longitudinal axis,whereby such shapes whose surfaces end towards the rake face with alarger radius than the upper areas, respectively flat or rectilinear incross section, are also included. At their ends directed towards thecutting edge and/or towards the middle of the cutting plate, the ribspreferably run at an acute angle to the rake face, which angle shouldnot exceed 20° in any actual embodiment of the invention. In theaforementioned configuration of the longitudinal ribs, the preferredshape of the base surface of the longitudinal ribs formed in the area ofthe rake face should be oval to elongated oval.

Along the respective cutting edge, the ribs can all be parallel to eachother, which includes a perpendicular direction with respect to thecutting edge, as well as a diagonal orientation, or they should bearranged in such manner that the groups of longitudinal ribs consistingof any other longitudinal ribs along a cutting edge are mutuallyparallel, running at a preferred angle of 1° to 45° to the plane normalto the cutting edge. This feature refers particularly to the arrangementof neighboring longitudinal ribs with respect to the normal plane of thecutting edge having the same absolute value but formed with anopposite-sense angle between 5° and 45°. This has the advantage that thecutting inserts can be inserted to turn to the left as well as to theright, whereby the chip control is each time achieved by the group oflongitudinal ribs arranged in direction of the chip flow.

In a further embodiment, the longitudinal ribs can be rectilinear orcurved preferably at a radius between 3 mm to 15 mm, from the point ofview of the axes of the longitudinal ribs. The aforementioned angles arethen selected towards the cutting edge as a discharge angle of thecurved longitudinal rib.

The shape of the longitudinal ribs can be also modified according to afurther embodiment of the invention, so that the longitudinal ribs haveat least one notch reaching all the way to the rake face. These notchesdivide the longitudinal ribs into several pieces arranged in a sequence,whereby the aforedescribed geometry of the solid-body longitudinal ribsis still valid regarding the envelope curve limiting all longitudinalribs. Due to the notches in the longitudinal ribs an additional increaseof the surface of the chip-forming elements is achieved, favoring theheat dissipation, without any influence of the notches on the chipformation and the chip control. Particularly the surfaces defining thenotches of the longitudinal ribs can be flat surfaces arranged at anacute angle towards the rake face, lying at an angle between 20° and 45°with respect to the rake face. Preferably the middle segments of thelongitudinal ribs have a trapezoidal shape. The distance between theindividual longitudinal ribs in a plane normal to the cuttingedge--respectively of each longitudinal rib thought of as an envelopecurve--preferably equals 0.2 to 1 mm.

As already mentioned before, the envelope curve formed by the respectivelongitudinal ribs arranged one after the other in the direction of theplane normal to the cutting edge is free of edges.

According to a further embodiment of the invention, particularly in thecase of longitudinal ribs with a rectilinear longitudinal axis, eachmiddle segment of the longitudinal ribs or the ends of the longitudinalribs can be offset with respect to the next longitudinal rib by onehalf-width of the distance.

According to further embodiments of the invention, the longitudinal ribsare arranged at various distances from the cutting edge or they can beof various lengths, whereby preferably the respective next longitudinalribs are located at the same distance from the cutting edge or are ofequal length. In this way it is possible to arrange a longerlongitudinal rib, divided by two notches into three pieces, next to ashorter longitudinal rib which is parallel thereto and wherein themiddle segment has been "omitted". This shorter longitudinal rib is thenoffset towards the cutting edge by half the length of the middle segmentof the longitudinal rib, thus being at a greater distance from thecutting edge.

Basically the chip-forming elements can be used in all known shapes andgeometries of indexable inserts. This applies particularly to suchcutting inserts which have a chamfer bordering along the cutting edge,which is free of chip-forming elements. This chamfer can run at an angleof 0°, but also at a positive or negative angle. According to furtherpossible developments of the invention, the rake face immediatelyfollowing the chamfer or the cutting edge can be curved, i.e. concave orconvex. The respective tangential angle of inclination is thereby of 5°to 30°. In a convex rake face, which in principle is designed as achip-breaking groove, the longitudinal ribs or the longitudinal ribsegments are arranged and dimensioned so that their upper edges do notexceed the surface formed by the cutting edges.

Various configuration possibilities can be considered also regarding theshape of the cutting edge. So for instance the cutting edge can beshaped from one cutting corner to the next cutting corner, i.e. in alateral view, convex, concave or as a free shape with a sinuous path.Also the lateral surface bordering the cutting edge can be designed as aclearance face.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIGS. 1a to 1g are different top views of cutting plates;

FIG. 2 is a detailed perspective view in the direction of arrow 2 ofFIG. 1a of a cutting plate corner;

FIG. 3a is a cross-sectional view perpendicular to the longitudinal axisthrough a chip-forming element according to the invention;

FIG. 3b is an enlarged detail view of an alternate arrangement of thelongitudinal ribs;

FIGS. 4a to 4e are detail views of rake face areas close to the cuttingedge, with longitudinal ribs having notches;

FIGS. 5a to c and FIGS. 6a to c are detail views of rake face areasclose to the cutting edge, with further embodiments of the longitudinalribs;

FIGS. 7a to 7c are diagrams of different shapes of cutting edges; and

FIG. 8a is an elevation and FIG. 8b a sectional view along lineVIIIb--VIIIb of FIG. 8a of an area close to the cutting edge seen in thelongitudinal direction of the longitudinal ribs.

SPECIFIC DESCRIPTION

FIGS. 1a-1g show examples of cutting inserts, each equipped with thechip-forming elements of the invention, as sketched with the aid of FIG.1a. So in FIG. 1a a cutting insert 10 with triangular base surface isshown. FIG. 1b shows a cutting plate 11 with six corners derived fromthe triangular base shape. FIGS. 1c and 1e show respective rhomboidalindexable inserts each with pairwise different, respectively identicaledge length. FIG. 1d shows a circular indexable insert 13. FIG. 1f showsa square-shaped indexable insert 15 with chamfered corners, while FIG.1g shows an indexable insert with two opposite curved edges 16a. Asindicated in FIGS. 1b, d and f, the cutting plate can also have acentral bore 33. As a rule, the invention can also be extended to othershapes of indexable inserts as known to the state of the art and whichare not illustrated here. The arrangement of the longitudinal ribs 17according to the invention is shown in FIG. 1a. Thereby the longitudinalribs are oriented so that their longitudinal axis is perpendicular tothe respective cutting edge. However, the longitudinal ribs can also beset diagonally, i.e. at an angle up to 45° to the plane normal to thecutting edge. As long as the cutting edges do not run in a straightline, as for instance in the case of a circular cutting plate 13, theorientation of the longitudinal ribs to the respective cutting edgetangent applies.

A detailed view of a cutting edge corner and the arrangement andconfiguration of the longitudinal ribs 17 of the invention, as indicatedby the numeral 2 in FIG. 1a, is shown in FIG. 2 with the modificationthat instead of a solid-body longitudinal rib 17, the latter is dividedby two notches 18 into three body segments 171, 172 and 173. Theenvelope surface of the segments bordering the longitudinal-rib segments171 to 173 has an edge-free convex contour and basically the shape of apartial ellipsoid of rotation, which is formed through a section along aplane parallel to the longitudinal axis. The base surface of each of thelongitudinal ribs 17 is in this case oblong-oval. The longitudinal ribs17 formed by the longitudinal-rib segments 171 to 173 are mutuallyparallel and perpendicular to the respective cutting edge 101. Thelargest base width b measured in the area of cut 18 of the middlelongitudinal-rib segment 172 ranges between 0.2 mm to 0.5 mm in cuttinginserts for milling tools, in the case of cutting tools for turning,respectively drilling, it ranges between 0.5 mm and 1.5 mm. The totallength of the longitudinal ribs amounts to about 5 times to 10 times thevalue of the mentioned base width b. The upper faces of the longitudinalribs 171 and 173 run on the rake face marked with 102 which surroundsthe longitudinal ribs, level towards the cutting edge 101 up to theopposite end, preferably at an angle of less than 20°. The cuts 18 areselected so that the bordering flat surfaces 20 and 21 on the one hand,as well as 22 and 23 on the other hand, are bevelled towards the rakeface 102, approximately at an angle of 30°. The distance z between theindividual longitudinal-rib segments 171 and 172, respectively 172 and173, measured in the area of the rake face 102 equals 0.2 to 1 mm, whilethe distance a between two neighboring longitudinal ribs 17 in millingtools lies between 0.5 to 1.5 mm and in turning or drilling toolsbetween 1.5 and 4 mm.

The contour of the cross section through the middle longitudinal-ribsegment 172 can be seen from FIG. 3a. In the upper area, the radius ofcurvature r is approximately of 0.3 mm, while the radius to the rakesurface 19, which here is flat, can be increased, possibly eveninfinitely large. The size of the angle y resulting from the position ofthe lower area with respect to a normal 24 is of at least 45°. The sizeof the angle x determined by the inclination angle of the lateralsurface segments 25 and 26 is of approximately 90°. The maximal height hof the longitudinal ribs is of 0.07 mm in milling tools and of 0.6 mm inturning tools. The preferred contour of the cross section remains theone shown in FIG. 3 (parallel to the cutting edge 101) and each distancebetween the cutting edges is basically preserved.

FIG. 3b shows a different kind of arrangement of the longitudinal ribs171 to 173, with respect to their diagonal position to the cutting edge101. The longitudinal axis 34 forms with the cutting edge 101 an anglewhich is larger than 45°. The longitudinal-rib segments 171 and 173 areshaped like wedges towards their ends marked with the reference numerals36 and 37, whereby the respective tangents 35 form with the longitudinalaxis an angle between 5° and 15°.

Further embodiments of the cutting insert shown in FIGS. 2 and 3 can beseen in FIG. 4. The longitudinal-rib segments 171 to 173 which can beseen there are arranged, from the point of view of their longitudinalaxis, in the direction of a line 28 perpendicular to the cutting edge101. However this line can also be curved (see FIG. 5a). Adjacent tothis cutting edge 101 there is a chamfer 27, which (see FIGS. 4c and d)runs horizontally (0° - orientation) or can have a positive or negativeangle. The thereto adjacent cutting edge 19 can be concave (FIGS. 4b tod) or convex (FIG. 4e). Also the longitudinal ribs 17, respectively thelongitudinal-rib segments 171 to 173 are adjusted to the contour of rakeface so that their base longitudinal axis assumes the same curvedconcave or convex course followed by the rake face 19. As shown in FIG.4b, the upper crest areas of the longitudinal-rib segments 171 to 173are limited by an envelope curve whose radius is larger than therespective radius of the surrounding rake face 19. However in themodification shown in FIG. 4c, the middle longitudinal-rib segment 172can project heightwise over the neighboring longitudinal-rib segments171 and 173.

In an alternate embodiment, according to FIG. 4c the middlelongitudinal-rib segment 172 projects in height over the respectiveneighboring longitudinal-rib segments; the same applies to the lastlongitudinal-rib segment 173 according to FIG. 4d with respect to thepreceding segments 172 and 171.

FIG. 4e shows a vaulted rake face, which continues edgelessly with thenegative chamfer 27 and whereupon the longitudinal-rib segments 171,172, 173 are arranged in succession. However, any other desired variantsof the individual features resulting from the drawing are also possible.

Further embodiment variants of the arrangement of the longitudinal ribsare illustrated in FIGS. 5a-5c and 6a-6c. So for instance according tothe top view in FIG. 5a the longitudinal-rib segments 171 to 173 are notrectilinear but follow a curved path 29. According to FIG. 5b the middlelongitudinal-rib segments 172 are staggered by a distance equal witha/2, so that immediately following the chamfer 27 there is a first rowof longitudinal-rib segments 171, each being parallel and at a distancefrom the cutting edge, but which are succeeded by a second row of middlelongitudinal-rib segments 172, whose configuration (see also FIG. 2) isapproximately trapezoidal seen in longitudinal cross section and whichin the cross section perpendicular thereto are shaped according to FIG.3a. In a third row the end-side longitudinal-rib segments 173 follow.

In the embodiment of FIG. 5e, longitudinal ribs 17 of various length andsubdivided in various ways are used. Any second of the longitudinal-ribsegments 171 to 173 are shown in accordance with the arrangement shownand described in FIG. 4a. In between and offset by a distance of a/2from the neighboring longitudinal-rib segments there are longitudinalribs 174 and 175, whose configuration corresponds to the one of thelongitudinal-rib segments 171 and 173. Between them a notch 18 isprovided, as shown and described in connection with FIG. 2. However inthe longitudinal rib 17 composed of longitudinal-rib segments 174 and175 the middle longitudinal-rib segment 172 has been altogethereliminated, which considerably shortens the length of this entirelongitudinal rib. Offset to the rear, towards the middle of the cuttingedge by half a length of the middle longitudinal-rib segment 172, thelongitudinal-rib segment 174 is correspondingly provided. Theembodiments shown in FIGS. 5b and 5c are not in any way limited to suchdesigns of the longitudinal ribs which are arranged perpendicularly tothe cutting edge. The respective longitudinal ribs can also be arrangedalong a curved path 29 (see FIG. 5a).

In FIG. 6 such arrangements of the longitudinal ribs 17a and 17b, whichare set diagonally to the plane normal to the cutting edge are provided,and namely in such a way that the respectively created angle has anopposite direction of rotation, as is indicated by the sign. Thisembodiment has the advantage that the respective cutting plate can beinserted for right as well as left turning. In a correspondingmodification according to FIG. 6b the longitudinal ribs 17a and 17binclined by an angle with respect to the absolute value do not lie on astraight line, but follow a curved path 29, which can be either convex(FIG. 6b) or concave (FIG. 6c). Even when in FIGS. 6a-6c longitudinalribs are shown which consist of three segments, the present inventionextends also to such longitudinal ribs which are made of more than threesegments succeeding each other, as well as to combinations according toFIGS. 4a-4e and 5a-5c.

The contour of the cutting edge from one cutting corner to the next canbe designed according to FIGS. 7a-7c to be positive (FIG. 7a), negative(FIG. 7b) or to have a free shape (FIG. 7c). The longitudinal ribs 17 asraised chip-formation elements can be designed either as solid bodies orseparated in segments by notches 18.

A cross-sectional view through the longitudinal axis of the longitudinalribs is shown in FIGS. 8a and 8b. The lateral surface is a clearanceface 31, succeeded in the area of the rake face at first by a chamfer 27with a width s, bordering on a convex rake face 32. The chamfer can alsobe eliminated, i.e. s=0 can be selected. The tangential angle ofinclination of the rake face 32 to the horizontally running chamfer 27 ,respectively to a corresponding horizontal line, can range between -150°and +20°. In the area of the convex rake faces 32, the longitudinal-ribsegments 171, 172 and 173 lie one after the other, their uppermost edgebeing clearly below the plane defined by the cutting edges 101. Thelongitudinal-rib segments 171 to 173 can run perpendicularly to thecutting edge 101, as well as at an acute angle on a straight or a curvedline.

We claim:
 1. A cutting insert for chip-forming machining, comprising:aninsert body having a cutting edge; and at least one rake face adjacentthe cutting edge and provided with a plurality of elongated raisedchip-forming ribs arranged as groups of ribs in respective rows at adistance from the cutting edge and extending along respective linesegments substantially perpendicular to the cutting edge or running atan acute angle (α) to a plane normal to the cutting edge, the linesegments of at least one of said groups of longitudinal ribs beingparallel to one another, each of said ribs being formed with arespective cross-section decreasing with distance from the rake face,each of said ribs being subdivided into a plurality of rib segments, therib segments of each of said ribs including two terminal segments spacedfrom one another and formed with respective inner faces defining atleast one notch between said terminal segments, the inner facesdiverging with respect to one another outwardly from said rake surfaceand transversely to the respective line segment, each of said innerfaces being the widest portion of the respective terminal segment at therespective notch, each of said terminal segments being generallysymmetrical with respect to the line segment and converging and taperingoppositely to respective points at the line segment.
 2. The cuttinginsert defined in claim 1 wherein the longitudinal ribs, transversely torespective segment lines, being formed with respective convexly andedgelessly shaped cross sections on the rake face.
 3. The cutting insertdefined in claim 2 wherein the respective cross section of each rib hasa convex shape so that a respective outer land spaced from said rakeface is formed with a radius (r) of 0.1 to 2 mm.
 4. The cutting insertdefined in claim 1 wherein, with respect to a plane normal to the rakeface, the longitudinal ribs run perpendicular to respective segmentlines in an area of the rake face at an angle (y) of at least 45° orhave wedge-shaped frontal ends or rear ends and run at a wedge angle. 5.The cutting insert defined in claim 4 wherein the longitudinal ribsterminate towards the rake face with a greater radius than in an upperarea or run evenly or in a straight line towards the rake face.
 6. Thecutting insert defined in claim 1 wherein each of the longitudinal ribshas a respective pair of side faces converging to one another at anangle (x) of 90° to 130° in a region of the rake fact.
 7. The cuttinginsert defined in claim 1 wherein a greatest base width of thelongitudinal ribs, measured in the area of the rake face is 0.2 to 0.5mm for milling tools and 0.5 to 1.5 mm for turning or drilling tools. 8.The cutting insert defined in claim 1 wherein a height (h) of thelongitudinal ribs is 0.02 to 0.07 mm for milling tools, or 0.1 to 0.6 mmfor turning, respectively drilling tools.
 9. The cutting insert definedin claim 1 wherein a length (l) of the longitudinal ribs is 5 times to20 times greater than a base width (b) thereof.
 10. The cutting insertdefined in claim 1 wherein a distance between two neighboringlongitudinal ribs is 0.5 to 1.5 mm for milling tools and for turningdrilling tools it is 1.5 to 4 mm.
 11. The cutting insert defined inclaim 1 wherein the ribs have the shape of a cap of an ellipsoid ofrotation, cut off in a plane parallel to the longitudinal axis.
 12. Thecutting insert defined in claim 11 wherein the longitudinal ribs, atends directed towards the cutting edge and/or towards a middle of thecutting plate, run with respect to the rake face at an acute angle ofless than 20°.
 13. The cutting insert defined in claim 1 wherein a basesurface of the longitudinal ribs formed in a region of the rake face isoval.
 14. The cutting insert defined in claim 1 wherein the parallelline segments run at an angle between 1° and 45° to said plane normal tothe cutting edge.
 15. The cutting insert defined in claim 1 whereinneighboring longitudinal ribs are arranged with respect to the planenormal to the cutting edge at an angle between 5° to 45°.
 16. Thecutting insert defined in claim 1 wherein the the segment lines run incurved line at a radius between 3 and 15 mm.
 17. The cutting insertdefined in claim 1 wherein the longitudinal ribs have at least one notchreaching all the way to the rake face.
 18. The cutting insert defined inclaim 17 wherein faces defining the notches of the longitudinal ribsform flat faces arranged at an acute angle to the rake face.
 19. Thecutting insert defined in claim 17 wherein distances (z) betweenlongitudinal-rib segments of a longitudinal rib determined by a commonenvelope curve range between 0.2 to 1 mm.
 20. The cutting insert definedin claim 17 wherein an envelope surface, formed by longitudinal-ribsegments and running in a direction of the plane normal to the cuttingedge, is edgeless.
 21. The cutting insert defined in claim 1 wherein thelongitudinal ribs taper downwardly toward the rake face at an acuteangle ranging between 20° to 45°.
 22. The cutting insert defined inclaim 1 wherein each of said ribs further has a respective anotherlongitudinal-rib segment located between a respective pair of terminalsegments and having a respective trapezoidal cross section.
 23. Thecutting insert defined in claim 22 wherein said each other segment isstaggered by half an interval width (a/2) with respect to a nextlongitudinal rib.
 24. The cutting insert defined in claim 23 wherein thelongitudinal ribs are arranged at different distances from the cuttingedge.
 25. The cutting insert defined in claim 24 wherein thelongitudinal ribs are of different lengths.
 26. The cutting insertdefined in claim 1 wherein along the cutting edge and bordering the samea chamfer is provided which is free of chip-forming elements.
 27. Thecutting insert defined in claim 26 wherein the chamfer runs at an angleof 0° to a positive, or negative angle.
 28. The cutting insert definedin claim 26 wherein the rake face adjacent to the chamfer is curved. 29.The cutting insert defined in claim 1 wherein the cutting edge, in aside view, has a convex or concave or sinuous shape.
 30. The cuttinginsert defined in claim 1 wherein the insert has lateral faces which areclearance faces.